Microplastics (MPs) are pervasive and undergo environmental aging processes, which alters potential interaction with the co-contaminants. Hence, to assess their contaminant-carrying capacity, mimicking the weathering characteristics of secondary MPs is crucial. To this end, the present study investigated the interaction of Zinc oxide (nZnO) nanoparticles with non-irradiated (NI) and UV-irradiated (UI) forms of the most abundant MPs, such as polypropylene (PP) and polystyrene (PS), in aqueous environments. SEM images revealed mechanical abrasions on the surfaces of NI-MPs and their subsequent photoaging caused the formation of close-ended and open-ended cracks in UI-PP and UI-PS, respectively. Batch-sorption experiments elucidated nZnO uptake kinetics by PP and PS MPs, suggesting a sorption-desorption pathway due to weaker and stronger sorption sites until equilibrium was achieved. UI-PP showed higher nZnO (∼3000 mg/kg) uptake compared to NI-PP, while UI-PS showed similar or slightly decreased nZnO (∼2000 mg/kg) uptake compared to NI-PS. FTIR spectra and zeta potential measurements revealed electrostatic interaction as the dominant interaction mechanism. Higher nZnO uptake by MPs was noted between pH 6.5 and 8.5, whereas it decreased beyond this range. Despite DOM, MPs always retained ∼874 mg/kg nZnO irrespective of MPs type and extent of aging. The experimental results in river water showed higher nZnO uptake on MPs compared to DI water, attributed to mutual effect of ionic competition, DOM, and MP hydrophobicity. In the case of humic acids, complex synthetic and natural water matrices, NI-MPs retained more nZnO than UI-MPs, suggesting that photoaged MPs sorb less nZnO under environmental conditions than non-photoaged MPs. These findings enhance our understanding on interaction of the MPs with co-contaminants in natural environments.

中文翻译：

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ZnO 纳米粒子在聚丙烯和聚苯乙烯微塑料上的保留：与老化相关的相互作用和水化学的作用


微塑料 (MP) 无处不在，并且会经历环境老化过程，从而改变与共污染物的潜在相互作用。因此，为了评估其污染物承载能力，模仿二级 MP 的风化特征至关重要。为此，本研究研究了氧化锌（nZnO）纳米颗粒与最丰富的MP（例如聚丙烯（PP）和聚苯乙烯（PS））的未辐照（NI）和紫外线辐照（UI）形式的相互作用，在水性环境中。 SEM 图像显示 NI-MP 表面的机械磨损及其随后的光老化分别导致 UI-PP 和 UI-PS 中形成封闭式和开放式裂纹。批量吸附实验阐明了 PP 和 PS MP 的 nZnO 吸收动力学，表明由于吸附位点较弱和较强而导致吸附-解吸途径直至达到平衡。与 NI-PP 相比，UI-PP 显示出更高的 nZnO (∼3000 mg/kg) 摄取量，而与 NI-PS 相比，UI-PS 的 nZnO (∼2000 mg/kg) 摄取量相似或略有下降。 FTIR 光谱和 zeta 电位测量表明静电相互作用是主要的相互作用机制。在 pH 值 6.5 至 8.5 之间，MP 对 nZnO 的吸收较高，但超出此范围则有所下降。尽管存在 DOM，MP 始终保留约 874 mg/kg nZnO，无论 MP 类型和老化程度如何。河水中的实验结果表明，与去离子水相比，MPs 对 nZnO 的吸收更高，这归因于离子竞争、DOM 和 MP 疏水性的相互作用。对于腐殖酸、复杂的合成和天然水基质，NI-MPs 比 UI-MPs 保留了更多的 nZnO，这表明光老化 MPs 在环境条件下比非光老化 MPs 吸附更少的 nZnO。 这些发现增强了我们对自然环境中 MP 与共污染物相互作用的理解。